The aim of the proposed research is the study of the effects of opiates on single neurons of the mammalian nervous system. The techniques used will be electrophysiological and histological. The excitable properties and synaptic connections of single neurons in discrete brain areas will be examined by intracellular recording. Slices of brain tissue including areas known to be rich in opiate receptors will be maintained in vitro. Opiates and opioid peptides will be applied by adding them to the perfusing solution and by microiontophoresis. The relevance of the observed effects will be tested by the use of appropriate known concentrations of different opiate agonists (including optical enatiomers) and specific opiate receptor antagonists. The role of endogenous opioid peptides will be examined both by applying them directly to the neurons and be observing the effects of opiate receptor antagonists (including optical enantiomers) on the electrical properties and synaptic connections of the neurons. The mechanism of action of opiates and opioid peptides will be investigated by changing the ionic environment. The effects of prolonged exposure to opiates in vivo will be examined in an effort to elucidate the changes in neuronal excitability which underlie tolerance and dependence. The proposed study represents a direct way to investigate the actions of opiates on single neurons from brain regions known to be important in opiate action. It avoids many of the pitfalls of in vivo extracellular recording yet it is more directly relevant than studies on peripheral tissues or cultured neuroblastoma cells. The results are expected to elucidate the primary actions of opiates on neurons, to differentiate between these actions and the longterm effects which form the basis of tolerance and dependence, and to establish any functional role of endogenous opioid peptides at the single neuron level.